Apparatus for cleaning a corona discharge strand

ABSTRACT

A corona discharge strand is cleaned by drawing the strand through a cleaning station having one or more brushes, such as felt pads, contacting the corona strand. In a preferred embodiment, the corona discharge strand is in the form of an endless loop wound at one end around a motorized capstan for drawing the strand to and fro or unidirectionally.

United States Patent 1191 2/l97l Salger 3l7/262 Hedman, 'Jr. [4 Oct. 8, 1974 [#541 gi giggg 3 :35 CORONA OTHER PUBLICATIONS I C. 1 s.h fi r Corona Unit Cleaning Device by W. F. Voit, Jr., [75] Inventor: clal'ence Hedman, Campbell from IBM Technical Disclosure Bulletin, Vol. I], No. callf' 8, Jan'. 1969, Page 1025. [73] Assignee: SCM Corporation, New York, N.Y. I v

. Primary Examiner-James W. Lawrence [22] m June 1973 Assistant Examiner-CE. Church [21] Appl. No.: 371,178 Attorney, Agent, or Firm-Armand G. Guib'ert; Milton I M. Wolson [52] U.S.'Cl 250/324, 250/325 51 1m. (:1 603g 15/00 ABSTRACT Field of Search A c rona discharge strand is cleaned drawing J 317/262 A strand through acTeanmg station having one or more brushes, such as felt pads, contacting the corona References lt strand. In a preferred embodiment, the corona dis 7 UNITED STATES PATENTS chang e strandjs in the form of an endless loopwouncl 2,81 1,135 10/1957 Hayford 250/324 at one @531 Oufiaa E1 7t5YiZa?@ta" TOY ar'mifih 2,856,533 10/1958 Rosenthal 1 20/325 trand to and fro or unidirectionally. 1

2/1970 Jugle; 250/326 9 Claims, 2 Drawing Figures charged.

I 1 APPARATUS'FOR CLEANING A CORONA DISCHARGE STRAND I BACKGROUND OF THE INVENTION The present invention relates in general to corona discharge apparatusand more particularly to an endless loop corona discharge strand and means for cleaning same.

DESCRIPTION OF THE PRIOR ART l-Ieretofore, endless loop corona discharge strands have been proposed for depositing a charge uniformly onto the surface of a member. Relative motionis effected between the corona discharge strand and the member to be charged, such relative motion being at right angles to the longitudinal axis of the strand for sweeping a relatively wide path across the member to be charged. It is also known that the endless loop corona discharge strand may be passed over a motorized pulley such that the strand ages uniformly so as to minimize failure and production of undesired streaking of the surface of the member being charged. Such a'moving corona discharge strand'is' taught in US. Pat. No.

v2,856,533 issued Oct. 14, 1958.

One of the problems encountered with corona charg- Referring now to FIG. 1, thereis shown an electro-v ing is that debris, such as toner particles, tend to accumulate on-the corona discharge strand. In the aforecited moving discharge strand, this debris is carried around with movement of the strand and any streaking or other nonuniformities in the charge distribution deposited upon the member being'charged merely shifts as the strand. is moved.

his also known from the prior art that, in the case of fixed corona discharge strands, the debris that tendsto cleaned by axial translation of the strand.

SUMMARY OF THE PRESENT INVENTION" Theprincipal object of the present invention is the provision of a corona" discharge apparatus having an improved means for cleaning the corona discharge strand.

In one feature of the present invention, a cleaning station isdisposed adjacent to the cor'ona discharge strand in such a manner .thatcleaningof the strand 'is' automatically produced upon axial translation of the strand for changing that portion of the strand which is effective for depositing charge onto the member to. be

In another featurelofthe present invention, the cleaning specification taken in connection with theaccom- FIG. 1 is a transverse schematic line diagram of an electrostatic copying machine incorporating features of DESCRIPTION OF THE PREFERRED EMBODIMENTS static copying machine 11 incorporating features of the present invention. The machine includes a drum 10 having a photoconductive outer cylindrical surface 12, as of selenium, to receive a charge image for development and subsequent transfer to a recording medium, as of paper. A corona charging station 13, preferably of the type more fully disclosed below in FIG. 2, deposits a'uniform charge background of a first polarity, either positive or negative, over the surface 12 of the drum'IO as it rotates past the corona charging station 13. Next, the background charge is dissipated from the photoconductive surface 12 of the drum 10 in accordance with an optical image projected onto surface 12 as it rotates past an exposure station 14. At the exposure' station l4,the surface 12 is rendered conductive in accordance with the optical image "projected onto the drum for dissipating charges on portions of the photoconductor corresponding to the illuminated portions ofthe image. Y

A development station 15 applies triboelectrically charged toner particles 24 in known fashion to the charge pattern on the drum 10 to produce a developed image which is then transferred to an insulative'recording'medium 16, as of paper, at an image transfer station 17. More particularly, the paper 16 is brought into contact with the developed image on drum 10. and a transfer corona of a high potential of opposite sign to that. of the charge on toner particles 24 is applied tothe back surface 16a of the insulated recording medium 16 such that the toner particles 24 of the developed image are transferred to the front surface 16b of paper 16 and held thereto via the transfer corona chargeplaced on the backside of paperl6. Thetransferred toner isthen subjected toheat at at fixing station 18 which causes, say, a thermo-setting coating on toner particles 24 to be melted, thereby fixing the image on paper 16, as is kn0WlI. Some of the toner particles 24 remain on surface 12 and thence pass under a. cleaning corona station 19 ing station for cleaning the corona discharge strand includes a pair of brushes pressing against the strand from opposite sides thereof. I v I In anotherfeature of the present invention, a corona discharge strand is drawn across a pair of bridge members to guide the strand during axial translation thereof and to hold the strand in precisely spaced relation from the surface tobe charged, despite any displacement forces generatedv by'the brushes of the cleaning station.

wherein surface 12=is again uniformly subjected to charges of a sign opposite to the sign of the charge on toner particles 24. Then drum 10 passes under a cleaning light station 21 which again uniformly discharges the charged surface of drum 10 to neutralize any charge remaining thereon. Next, drum 10 passes under a cleaning brush station 22 wherein the remaining toner particles 24 are brushed from thesurface 12 of drum 10. The'cleaned'portion of surface 12 is then in a condition for repetition of the operating cycle;

Referring now to FIG. 2, there is shown a corona charging station-25 of a type useful for chargingat sta-' tions l3, l7, and 19 of FIG. 1. Corona charging station 25 includes an endless loop corona strand 26 as of wire,-

wrapped around and extending between a pair of rotatable members 27 and 28, respectively. Rotatable member 27 is not merely an idler pulley, as it also serves for making electrical contact to corona strand 26, being made of an electrically conductive material such as aluminum. A power supply 29 is connected to pulley 27 via an electrical contactor finger 31 riding on an axle I 32 supporting pulley 27. A pair of tensioning springs 33 are also affixed to axle 32 for biasing pulley 27 outwardly of the endless loop of the corona strand 26 for holding the strand in tension.

Corona strand 26 is looped around the other rotatable member 28 which serves as a capstan. The length of corona strand wound on capstan 28 is preferably longer than the effective corona discharge length of corona strand 26, as more fully described below. it will be obvious to those skilled in the art that the member 27 could be fixed rather than rotatable and strand 26 allowed to slide over it, contact 31 then being replaced by a solid connection.

In one embodiment, corona strand 26 is formed into the endless loop by tying together the ends of the strand to form a knot 35. In an alternative embodiment (not shown), strand 26 is a wire welded together at its ends to form the endless loop and then ground in such a way that at the point where the two ends of the wire are joined together the wire diameter is not appreciably increased.

A pair of insulative bridges 36, as of Teflon (TM), are disposed on opposite sides of the effective active area of corona strand 26, such bridges 36 extending laterally of the strand 26 and serving to space strand 26 a precise distance away from the surface of the member to be chared such as the photoconductive surface 12 or the back surface 16a of insulated paper sheet l6.-The plane of the endless loop 26 is arranged to be parallel to the surface to be charged, either 12 or 16a, which surface moves laterally relative to the longitudinal axis of strand 26. Thus the effective length of strand 26 is that length which extends between the bridges 36 and is coextensive with the surface 12 or 16a to be charged.

Two pairs of elongated cleaning brushes 37, such as Teflon-backed felt or plastic foam, are disposed outwardly of and parallel to each of the bridge members 36. The cleaning brushes 37 are fixed in position and, at each cleaning station, press against the corona strand 26 from opposite sides thereof such that the felt or foam portion of the brushes 37 essentially envelopes the corona strand 26. In use, as mentioned previously, toner particles 24 and other debris tend to collect on strand 26 and this collection of debris disturbs the uniformity of the corona discharge region in such a manner as to cause streaking of the charge pattern deposited upon the surface being charged.

At each corona cleaning station (pair of brushes), the brushes 37 are offset from each other axially of the strand 26 such that the strand is partially curved or wrapped around each of the brushes 37 to obtain a more complete cleaning action. The displacement of corona strand 26 from the plane of the endless loop by means of the brushes 37 produces, at each cleaning station, equal and opposite displacements such that the mean displacement of strand 26 from the plane of the 6 endless loop is negligible. The bridges 36 are preferably notched in alignment with the strand 26 to facilitate guiding and precise positioning of the strand 26.

The capstan 28, in a preferred embodiment, is power driven via drive motor 38, such as a stepping motor or a continuous drive motor, the drive connection being made through an insulated shaft 50. In the case where strand 26 is welded together or otherwise joined without the provision of a knot, the drive motor 38 merely rotates capstan 28 in one direction to cause corona strand 26 to be axially translated such that it wears or ages uniformly and at the same time strand 26 is cleaned automatically by brushes 37.

In the case where a knot 35 is employed to join the ends of strand 26, knot 35 would produce a nonuniform region in the charge pattern deposited upon the surface to be charged if the knot appeared in that area. Accordingly, the endless loop is arranged so that knot 35 is disposed between a pair of lever actuated microswitches 41,41. The lever portions 42,42 of microswitches 41,41 include guide slots 44,44 through which-the strand 26 slides. The slots 44,44 are dimensioned so that knot 35 will not pass therethrough but instead will deflect lever 42 in such a way as to actuate switch 41, or lever 42 to actuate switch 41. The switches 41,41 control the direction of rotation of the motor 38 in known fashion.

ln operation, assuming the knotted loop comprising strand 26 is operating in the counterclockwise direction, the knot 35, upon encountering lever 42, actuates microswitch 41' to cause a reversal in the direction of rotation of capstan 28. Capstan 28 then continues to drive strand 26 in the opposite (clockwise) direction until knot 35 encounters lever 42 at which point it actuates'microswitch 41 to again reverse the direction of rotation of motor 38 and capstan 28, therefore. In this manner the knot portion 35 of the endless loop oscillates back and forth around capstan 28 between the two levers 42,42 over a distance at least equal to the distance between the cleaning brushes 37,37. Thus knot 35 never rides over the surface being charged though the effective active area of strand 26 is cleaned.

in a manually operated embodiment, a crank 43 is connected to capstan 28 such that corona strand 26 may be manually operated. If desired, particularly in the case of the use of a stepping motor as drive motor 38, the rate of axial translation of the corona strand 26 can be coordinated with the rate at which copies are being produced.

The advantage of the corona charging station 25 of the present invention is that corona strand 26 is automatically cleaned as it is axially translated for achieving uniform wear and aging of the strand.

What is claimed is:

1. In a corona discharge apparatus:

a corona discharge strand having at least one axial portion effective for depositing charge onto the surface of a member moving relative to said corona discharge strand and having another portion thereof remote from said surface;

means for effecting axial translation of said strand for changing that portion of the strand effective for depositing charge onto said surface, said means for effecting axial translation including first and second spaced rotatable members;

a junction forming said strand into an endless loop around said rotatable members and being part of the remote portion of the strand, the junction being substantially larger than the strand;

means for sensing the junction;

control means responsive to sensing of the junction and alternately effecting said translation in opposite directions;

means disposed adjacent the strand for cleaning accumulated debris therefrom in response to axial translation of the strand.

2. The apparatus of claim 1 wherein said strand cleaning means comprises a pair of brushes pressing against the strand from opposite sides of the strand.

3. The apparatus of claim 2 wherein said pair of brushes are offset from each other axially of said strand.

4. The apparatus of claim 1 including a pair of bridge members bearing against said strand and being spaced apart axially of the strand to define said effective charge depositing portion of the strand therebetween.

5. The apparatus of claim 1 wherein said translation means comprise drive means coupled to said first rotatable member.

6. The apparatus of claim 5 wherein said second rotatable member is electrically conductive, and further including a power source for supplying a coronaproducing electric potential, and means for applying said corona-producing electrical potential to said strand through said second rotatable member.

7. The apparatus of claim 5 wherein said remote portion of the strand is substantially wound around said first rotatable member and comprises at least one turn, and first and second laterally-spaced parts of said loop define a pair of effective charge-depositing lengths of said strand, the'wound'portion of the strand being of a length such that the junction is sensed only after cleaned lengths of strand lie adjacent the surface of said moving member.

8. The apparatus of claim 7 wherein said junction is a knot and said drive meansis a reversible motor having an output drive shaft coupled to said first rotatable member and further including a reversing control for the motor, comprising a pair of switches each having an actuator with a slotted end straddling a respective part of the remote portion of the strand and being effective to engage said knot as the strand is translated.

9. In an electrostatic copy production machine:

a corona discharge strand having at least one axial portion effective for depositing charge onto the surface of an imaging member positioned proximate said axial portion of the corona discharge strand and having another portion thereof remote from said imaging member;

means for effecting relative movement of said imaging member laterally of said strand;

means for effecting axial translation of the strand for changing that portion of the strand effective for depositing charge onto the imaging member, said means for effecting axial translation including first and second rotatable members, at least one of the rotatable members being driven during copy production;

a junction forming said strand into an endless loop around said rotatable members and being part of the remote portion of the strand, the junction being substantially larger than the strand;

means for sensing the junction;

control means responsive to sensing of the junction and alternately effecting said translation in opposite directions;

means disposed adjacent the strand for cleaning accumulated debris therefrom in response to axial translation of the strand;

means for forming a charge image pattern on the imaging member; and

means for developing said charge image pattern. 

1. In a corona discharge apparatus: a corona discharge strand having at least one axial portion effective for depositing charge onto the surface of a member moving relative to said corona discharge strand and having another portion thereof remote from said surface; means for effecting axial translation of said strand for changing that portion of the strand effective for depositing charge onto said surface, said means for effecting axial translation including first and second spaced rotatable members; a junction forming said strand into an endless loop around said rotatable members and being part of the remote portion of the strand, the junction being substantially larger than the strand; means for sensing the junction; control means responsive to sensing of the junction and alternately effecting said translation in opposite directions; means disposed adjacent the strand for cleaning accumulated debris therefrom in response to axial translation of the strand.
 2. The apparatus of claim 1 wherein said strand cleaning means comprises a pair of brushes pressing against the strand from opposite sides of the strand.
 3. The apparatus of claim 2 wherein said pair of brushes are offset from each other axially of said strand.
 4. The apparatus of claim 1 including a pair of bridge members bearing against said strand and being spaced apart axially of the strand to define said effective charge depositing portion of the strand therebetween.
 5. The apparatus of claim 1 wherein said translation means comprise drive means coupled to said first rotatable member.
 6. The apparatus of claim 5 wherein said second rotatable member is electrically conductive, and further including a power source for supplying a corona-producing electric potential, and means for applying said corona-producing electrical potential to said strand through said second rotatable member.
 7. The apparatus of claim 5 wherein said remote portion of the strand is substantially wound around said first rotatable member and comprises at least one turn, and first and second laterally-spaced parts of said loop define a pair of effective charge-depositing lengths of said strand, the wound portion of the strand being of a length such that the junction is sensed only after cleaned lengths of strand lie adjacent the surface of said moving member.
 8. The apparatus of claim 7 wherein said junction is a knot and said drive means is a reversible motor having an output drive shaft coupled to said first rotatable member and further including a reversing control for the motor, coMprising a pair of switches each having an actuator with a slotted end straddling a respective part of the remote portion of the strand and being effective to engage said knot as the strand is translated.
 9. In an electrostatic copy production machine: a corona discharge strand having at least one axial portion effective for depositing charge onto the surface of an imaging member positioned proximate said axial portion of the corona discharge strand and having another portion thereof remote from said imaging member; means for effecting relative movement of said imaging member laterally of said strand; means for effecting axial translation of the strand for changing that portion of the strand effective for depositing charge onto the imaging member, said means for effecting axial translation including first and second rotatable members, at least one of the rotatable members being driven during copy production; a junction forming said strand into an endless loop around said rotatable members and being part of the remote portion of the strand, the junction being substantially larger than the strand; means for sensing the junction; control means responsive to sensing of the junction and alternately effecting said translation in opposite directions; means disposed adjacent the strand for cleaning accumulated debris therefrom in response to axial translation of the strand; means for forming a charge image pattern on the imaging member; and means for developing said charge image pattern. 